Yume Miru Kusuri hilariously interrupts your first h-scene — the protagonist is about to put it in (on the school roof…), then goes, “Shit, better buy a condom! Be right back!” and rushes to a convenience store.

No, it has to do with the reluctance of people to have children or only having a single child. Alongside the “you still have lotsa time to have children” phrase that’s constantly told to women even if they’re 30~.
People would’ve to get away from the thought that one child would be normal and two children would be a alot.

TBH I am curious as to why pregger endings are on the rise in visual novels like these?

Sure if it was outright hentai it’d be much easier to understand. I have nothing against pregnant girls/women but these kinds of endings seems forced. Maybe I’m just used to seeing preggo characters in the long run of a story rather than a result in an ending. Usually it’s the baby in arms to state the obvious.